The present invention relates to anti-crevice corrosion sealants for metals which can restrain crevice corrosion occurring at fine crevices formed between the elements of metal machinery and tools or on the jointed interior surface of the elements.
It is known that corrosion, referred to as "crevice corrosion" in the art occurs at fine crevices between the elements of metal machinery and tools, for example, the joined interior surfaces of flanges or the crevice between the screw surface of a bolt and a tapped hole when said metal machinery and tools are used in water or sea water (hereinafter referred to simply as "sea water, etc."). This phenomenon appears particularly remarkably in sea water rather than in fresh water and in the case of stainless steel or aluminum which are easy to be brought to a passive state.
It is considered that one reason for the crevice corrosion is an oxygen concentration cell action due to a difference between the oxygen concentration in the liquid present in crevices and the oxygen concentration at parts remote from crevices. Further, a reduction of the pH of the liquid in crevices due to the dissolution of the metal surface is considered to be another reason therefor.
As a process for restraining crevice corrosion, there have heretofore been known a process which comprises coating a paint onto the head of a bolt after bolting and a process which comprises covering the head of a bolt with a lining material. According to the process which comprises coating a paint, however, it is inevitable that the liquid penetrates into the crevices after use for a long period of time. Such is also the case with the process which comprises covering with a lining material. In both of the processes, crevice corrosion occurs. Further, there are a process which comprises adding a cation exchange substance into crevices to remove chloride ion and restrain crevice corrosion, a process which comprises applying a sheet impregnated with an alkali such as sodium silicate to crevices and prevent the acidification of the liquid in the crevice, and a process which comprises adding an inhibitor of chromate and bichromate series, nitrate series or primary, secondary and tertiary phosphates series to crevices. However, all the processes can not obtain a satisfactory anticorrosion effect.
Therefore, an object of the present invention is to obviate the above-mentioned defects of prior art anti-crevice corrosion sealants (hereinafter referred to simply as "sealants") for metals.
Another object of the invention is to provide a sealant for metals which can restrain the occurrence of crevice corrosion by filling it into crevices.
The other objects and advantages of the present invention will be apparent from the following description.